How many miles does it usually take for the monitors on a 96 Explorer to complete all tests after clearing the OBDII codes?

All but the evap and catalyst moniters should clear in about 10 miles. You need a mix of in town and highway driving. The catalyast should clear next. It sometimes takes me as much as 20 miles. The evap maoniter, I usually dont even try, because I have driven them for 40 miles and still to no avail. Remember though to check your pending codes, because when a monter won't clear it is often because there is a problem, and there is a pending code in there.